hallo guys, I use a gas engine to drive a synchronous generator. But I have a problem about how to avoid the 15% overspeed by changing the last from 100% to 0%.

When the load from 100% to 0% changes, at the same time I also completely close the throttle, because of the large mass of the generator rotor, it means there is great inertia, so the speed rapid increased and reached 14.5% overspeed. It is already close to the 15% overspeed protection.

If I use the speed governor instead, the throttle cannot be immediately completely closed by loss of the full load. More than 15% overspeed will occur in such a situation. Could anyone have some ideas or solutions for that?

 

Normally the GT is programmed to accelerate and decelerate slowly by increasing the fuel staging valves opening and closing time. This protection has to be modified for "Island Test Mode".

Inertia alone cannot increase the speed. It is the torque that tries to remain constant in the GT on the sudden No-load or Island condition. As there is no load, the torque tends to speed up the GT and the frequency at the GTG increases beyond safety levels.

You should also make sure that there is a path for the GTG to give out the power it is producing internally within the plant, when you cut it from the Grid during an Island Mode.

Because of the sudden loss of demand, the fuel gas flow stalls and pressure builds up in buffer chamber at the GT. This sudden rise should be regulated as well. Closing valves temporarily from the Fuel Gas Compressor can also help regulate the speed.

This should similar for all gas based Power Plants.